Abstract
Abstract. We investigated concentrations of organic carbon (OC), elemental carbon (EC), and a wide range of particle-bound organic compounds in daily sampled PM2.5 at the remote Pha Din (PDI) – Global Atmosphere Watch (GAW) monitoring station in northwestern Vietnam during an intense 3-week sampling campaign from 23 March to 12 April 2015. The site is known to receive trans-regional air masses during large-scale biomass burning (BB) episodes. BB is a globally widespread phenomenon and BB emission characterization is of high scientific and societal relevance. Emissions composition is influenced by multiple factors (e.g., fuel and thereby vegetation type, fuel moisture, fire temperature, available oxygen). Due to regional variations in these parameters, studies in different world regions are needed. OC composition provides valuable information regarding the health- and climate-relevant properties of PM2.5. Yet, OC composition studies from PDI are missing in the scientific literature to date. Therefore, we quantified 51 organic compounds simultaneously by in situ derivatization thermal desorption gas chromatography and time-of-flight mass spectrometry (IDTD-GC-TOFMS). Anhydrosugars, methoxyphenols, n-alkanes, fatty acids, polycyclic aromatic hydrocarbons, oxygenated polycyclic aromatic hydrocarbons, nitrophenols, and OC were used in a hierarchical cluster analysis highlighting distinctive patterns for periods under low, medium, and high BB influence. The highest particle phase concentration of the typical primary organic aerosol (POA) and possible secondary organic aerosol (SOA) constituents, especially nitrophenols, were found on 5 and 6 April. We linked the trace gas mixing ratios of methane (CH4), carbon dioxide (CO2), carbon monoxide (CO), and ozone (O3) to the statistical classification of BB events based on OA composition and found increased CO and O3 levels during medium and high BB influence. Likewise, a backward trajectory analysis indicates different source regions for the identified periods based on the OA clusters, with cleaner air masses arriving from the northeast, i.e., mainland China and the Yellow Sea. The more polluted periods are characterized by trajectories from the southwest, with more continental recirculation of the medium cluster and more westerly advection for the high cluster. These findings highlight that BB activities in northern Southeast Asia significantly enhance the regional organic aerosol loading and also affect the carbonaceous PM2.5 constituents and the trace gases in northwestern Vietnam. The presented analysis adds valuable data on the carbonaceous and chemical composition of PM2.5, in particular of OC, in a region of scarce data availability, and thus offers a reference dataset from Southeast Asian large-scale BB for future studies. Such a reference dataset may be useful for the evaluation of atmospheric transport simulation models, or for comparison with other world regions and BB types, such as Australian bush fires, African savannah fires, or tropical peatland fires.
Highlights
Biomass burning (BB) is a globally widespread phenomenon, and emissions characterization is of high scientific and societal relevance
The temporal trend of organic carbon (OC) and elemental carbon (EC) correlated with the observed levoglucosan (LEV), which is known as a marker of biomass burning (BB) (Simoneit et al, 1999), pointing towards the substantial influence of BB on the carbonaceous aerosol content
Our extensive characterization of carbonaceous PM2.5 species and monitoring of trace gases at the Pha Din (PDI) station in Vietnam from 23 March to 12 April 2015 gives insights into the atmospheric composition during the pre-monsoon season, which is impacted by large-scale open biomass burning (BB) on mainland Southeast Asia
Summary
Biomass burning (BB) is a globally widespread phenomenon, and emissions characterization is of high scientific and societal relevance. Fires release pollutants which are harmful for human and ecosystem health (Stott, 2000; Kanashova et al, 2018; Pardo et al, 2020; Ihantola et al, 2020) and alter the Earth’s radiative balance (Che et al, 2021; Lu et al, 2015) Those fires, for instance, emit substantial amounts of carbon monoxide (CO), various volatile organic compounds (VOCs) of diverse chemical reactivity and level of harmfulness, and carbonaceous particulates such as elemental carbon (EC) and primary organic aerosol (POA) (Akagi et al, 2011; Aurell and Gullett, 2013; Popovicheva et al, 2017a). Due to regional variations in these parameters, studies in different world regions are needed
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